1. Field of the Invention
This invention relates to a data processing apparatus and, more particularly, to a data processing apparatus having function for retrieving abstract and original image data.
2. Description of the Related Art
To cope with the large volume of documents generated in modern offices and factories, a data processing apparatus for electronically filing documents containing literal and drawing information has been developed, and is referred to as an electronic filing apparatus. A document inserted into such a filing apparatus, is optically scanned in a two-dimensional manner, and the image data obtained thereby are stored in a large-capacity memory device such as an optical disk. When a copy of a specific document is needed at a later time, the data thereof is retrieved from storage. This type of apparatus is disclosed in U.S. Pat. No. 4,661,988, for example.
The recent trend is that a plurality of image data filing apparatuses are connected, thus forming a so-called local area network (LAN), so that data can be retrieved from one apparatus and stored into another apparatus. The other recent trend is that the image data filing apparatuses file documents of greater sizes than before. This is because, now data is printed not only on A3-size paper, A4-size paper, B4-size paper, which are generally used in offices, but also on paper of greater sizes, such as A1-size paper and A2-size paper.
Here arises a problem with a stand-alone filing apparatus. The greater the document size, the longer time is required to retrieve the document from the filing apparatus. In particular, it takes an extremely long time to retrieve data equivalent to a A1-size or A2-size document from the filing apparatus.
More specifically, the image data printed at the density of 200 ppi (8 lines/mm) on an A4-size document is represented by 500 KB. This data can be compressed or reduced to about 50 KB by means of MR (modified read) technique. On the other hand, the image data printed at the density of 400 ppi (16 lines/mm) on an A1-size document is represented by 16 MB. This large amount of data can be compressed or reduced to about 1.6 MB, about 30 times greater than the compressed A4-size image data. A stand-alone data filing apparatus needs about 0.5 seconds to retrieve A4-size image data (200 ppi), and about 15 seconds to retrieve A1-size image data (400 ppi). In addition, it takes about 10 seconds to transfer the A4-size image data, and about 300 seconds to transfer A1-size image data, from one stand-alone data filing apparatus to another.
In short, the greater the image data, the longer the time required to retrieve the data from a stand-alone data filing apparatus and transfer it to another stand-alone data filing apparatus. Neither the data-retrieving time nor the data-transferring time can be shortened even if the CODEC circuit for compressing data and the data-transfer system are improved.
Here, the stand-alone filing apparatus cannot work so efficiently or so economical as is now demanded, due to the long time required to retrieve data and transfer the data to another stand-alone filing apparatus. Further, the present technology is unable to provide a data filing apparatus which can retrieve image data, one A1-size (or A2-size) document after another.